Re: Suspended floor sistering

[Mrxman]

I about to order some 100 x 47 timber for sistering joists on suspended floor.

The floor joists in one room are generally in good condition but as you can see from the picture they are made of two pieces of timber, joined in the middle. Because the wall plate is slightly bend some of the joists are a bit higher and some a bit lower where they join which makes for a slightly uneven floor at that particular spot.

Any thoughts on how to fix this?

I was thinking of sistering the joist, possibly one on each side. But how long should it be?

Any advice greatly appreciated

Thanks

 

[Deleted member 174758]

100 x 47 (or ex-4 x 2) seems a bit on the small side for sistering, are your joists really only 4 x 2 in? (Sistering should be the same depth and ideally the same thickness as the existing joists). When sistering joists it is normal to drill through both the joists and fix them together using coach bolts and a washer ideally with a star washer in the middle of each bolt. These should be at centres not exceeding 600mm. The sistering joists must be the same length as the existing joists and ideally need at least 50mm bearing either into a wall pocket (in which case if the wall is external thevends of the joists additionally need to be envelope wrapped in roofing felt to prolong their lifespan - they should also be treated timbers) or onto a timber bearer affixed to beam, wall or the like.

 

[Mrxman]

100 x 47 (or ex-4 x 2) seems a bit on the small side for sistering, are your joists really only 4 x 2 in? (Sistering should be the same depth and ideally the same thickness as the existing joists). When sistering joists it is normal to drill through both the joists and fix them together using coach bolts and a washer ideally with a star washer in the middle of each bolt. These should be at centres not exceeding 600mm. The sistering joists must be the same length as the existing joists and ideally need at least 50mm bearing either into a wall pocket (in which case if the wall is external thevends of the joists additionally need to be envelope wrapped in roofing felt to prolong their lifespan - they should also be treated timbers) or onto a timber bearer affixed to beam, wall or the like.

The existing joists are actually (100 x 50). The joists I was thinking of buying are (97 x 47), so a few millimeters short. Standard measurements it seems. Was thinking of using wood shims.
How you describe sistering is how I was thinking about going about it. The joists in the picture are generally o.k but as mentioned they're slightly different height where they're joined and wondering if it would be worth the trouble and expense fixing it with full length sistering joists.

 

[Deleted member 174758]

In the case of a break like that, yes.